This invention relates to measuring systems, and more particularly to an optically based system for non-contact measurement of a part such as an airfoil having a complex part shape. Because the shape of an airfoil is complex it has a critical bearing on the performance of an engine in which it is installed. Airfoil shape is defined by a CAD definition in terms of sections, or a three dimensional (3D) surface characterized by a number of parameters which include contour, bow, and warp. Current methods inspecting airfoils utilize dedicated hard gauges or coordinate measuring machines (CMMs). Both methods determine whether or not an airfoil falls within drawing specified limits for contour, bow, twist and chord, as well as other parameters.
There are a number of problems associated with these inspection methods. First, hard gauges are expensive, slow to manufacture and dedicated to a single airfoil shape. Manufacturing shops must store and perform regular maintenance on all their hard gauges. Second, a significant amount of time is required to inspect an airfoil. In a manufacturing environment, increasing the speed of inspection (so long as inspection accuracy is not compromised) can provide significant cost savings. Another factor is the reliability of the inspection results. With complex surface shapes such as airfoils have, small errors in the use of hard gauges or CMMs may result in acceptable parts being rejected, or unacceptable parts being accepted. Related to this third factor is need to have reliable inspection data available for analysis to both monitor the manufacturing process to improve both the process and the parts produced.
Given the above, it would be advantageous to have available an improved inspection method which facilitates lower gauge cost and quicker part inspection while providing highly accurate and reliable test results.
The present invention utilizes one or more non-contact sensors, in combination with appropriate data acquisition systems and data processing, to inspect the surface shape of an airfoil, determine its manufactured parameters, and compare the acquired shape data to specified limits to determine if the airfoil meets acceptance criteria. The advantage of using non-contact inspection methods is that the speed of inspection can be increased, results are more reliable because the process is automated, and quantitative data relating to airfoil shape is immediately available for use in monitoring the manufacturing process as well as for future use in making design improvements.
A wide variety of non-contact sensors are commercially available, and are readily integrated into systems performing non-contact measurement of physical objects. Despite this, however, many previous attempts to measure airfoil parameters using these sensors have failed because of i) the measurement system's inability to meet accuracy and speed requirements, and ii) difficulties related to effects of the airfoil's surface finish on optically measuring the surface characteristics of the airfoil.